I am married to a sunni man and every Ramadhan we are having problems considering time of opening the fast he wants me to open the fast on the same time as he does. If i dont he ends up getting angry and annoyed with me. What do I do? Can I open the same time as he does or is it not allowed?

I pray to Allah to make it easy for you. You are not allowed to open at that time. You only open your fast when there is darkness.
Your husband should not have a problem since he knows you are a Shia.